The campaign to save the Glenside Hospital Trees took a political hit this afternoon in State Parliament as the Liberal Party sided with Labor and voted "no objection" to the rezoning of the land for 1,000 apartments.

"The Liberals have sided with Labor and placed the trees on the chopping block in the process," Greens Parliamentary Leader, Mark Parnell MLC, said.

"Had the Libs voted with the Greens instead, we could have stopped the rezoning and brought some valuable bargaining leverage to halt the destruction of the trees and force the developer back to the drawing board to incorporate more of these magnificent trees into their designs."

Developer Cedar Woods has applied to destroy 83 "significant & regulated trees", each with a girth of at least 2 metres, so they can build 1,000 private apartments on the Glenside Hospital site.

"The community has every right to be disappointed that the Liberals have blown their chance to stand up for the Glenside trees. It makes a mockery of their supposed support for the community campaign at public meetings and in the media," Mr Parnell continued.

"This isn't about whether houses will be built on public land at Glenside - that battle was lost years ago. It's now about preserving the site's best features, which include these wonderful trees, many over 100 years old.

"The developer should be made to incorporate as many of these trees as possible into the apartment complex. That will be good for the environment, good for future residents and good for the local community.

"The Greens will continue to push for more sensible planning outcomes. We'll also be supporting local residents in their bid to save the trees at a hearing of the Development Assessment Commission expected later this month," he concluded.